1. Field of the Invention
The invention relates to the preparation of molybdenum/alkali metal/ethylene glycol complexes and to the manufacture of propylene oxide and tertiary butyl alcohol by the molybdenum/sodium/ethylene glycol catalyzed reaction of propylene with tertiary butyl hydroperoxide useful as olefin epoxidation catalysts.
2. Prior Art
The epoxidation of olefins to give various epoxide compounds has long been an area of study by those skilled in the art. It is well known that the reactivities of the various olefins differ with the number of substituents on the carbon atoms involved in the double bond. Ethylene itself has the lowest relative rate of epoxidation, with propylene and other alpha olefins being the next slowest. Compounds of the formula R.sub.2 C.dbd.CR.sub.2, where R simply represents alkyl or other substituents, may be epoxidized fastest. Thus, the more substituents on the double bond carbons, the easier it is to epoxidize across that bond.
The production of ethylene oxide from ethylene has long been accomplished by reaction with molecular oxygen over a silver catalyst. Numerous patents have issued on various silver-catalyzed processes for the production of ethylene oxide. Unfortunately, the silver catalyst route will not work for olefins other than ethylene. For a long time the commercial production of propylene oxide could only be accomplished via the cumbersome chlorohydrin process.
Another commercial process for the manufacture of substituted epoxides from alpha olefins such as propylene was not discovered until John Kollar's work in the 1960s. His U.S. Pat. No. 3,351,635 taught that an organic epoxide compound could be made by reacting an olefinically unsaturated compound with an organic hydroperoxide in the presence of a molybdenum, tungsten, titanium, columbium, tantalum, rhenium, selenium, chromium, zirconium, tellurium or uranium catalyst. Kollar's U.S. Pat. No. 3,350,422 teaches a similar process using a soluble vanadium catalyst.
The Kollar process is a coproduct process wherein the olefin and the hydroperoxide are catalytically reacted to provide an epoxide corresponding to the olefin and an alcohol corresponding to the hydroperoxide. A wide variety of epoxides and alcohols can be prepared in this manner. The process is practiced commercially in the manufacture of propylene oxide from propylene.
Kollar's work has been recognized as extremely important in the development of a commercial propylene oxide process that did not depend on the chlorohydrin route. It has been recognized that Kollar's catalytic route (in which a soluble molybdenum compound is the preferred catalyst) has a number of problems. For example, when propylene is the olfin to be epoxidized, various propylene dimers, sometimes called hexenes are formed as byproducts. Besides being undesirable in that the best use of propylene was not made, problems are encountered in separating the desired propylene oxide from the product mix. In addition, the molybdenum catalyst may not be stable or the recovery of the catalyst for recycle may be poor.
Various avenues of investigation have been explored in attempts to improve on the molybdenum-catalyzed epoxidation of propylene. One technique was to try to improve on the catalyst itself. Patents which cover the preparation of various molybdenum epoxidation catalysts include U.S. Pat. No. 3,362,972 to Kollar. There a hydrocarbon soluble salt of molybdenum or vanadium may be made by heating a molybdenum compound in which molybdenum has a valence of +6, or a vanadium compound in which vanadium has a valence of +5, with a carobxylic acid of from 4 to 50 carbon atoms having at least 4 carbon atoms per carboxylic group. U.S. Pat. No. 3,578,690 to Becker discloses that molybdenum acid salts may be made by directly reacting a carboxylic acid with a molybdenum compound while removing the water that is formed.
The reaction of molybdenum trioxide with monohydric saturated alcohols having 4 to 22 carbon atoms or with a mono- or polyalkylene glycol monoalkyl ether or mixtures thereof to make olefin epoxidation catalysts is described in U.S. Pat. No. 3,480,563 to Bonetti et al. These catalysts have only 0.07 to 0.93% molybdenum, which is a molybdenum content too low for commercial use. Bonetti et al. do not realize the importance of the ratio of alcohol to molybdenum compound reactants with respect to maximizing molybdenum content yet providing a soluble, active epoxidation catalyst. They also do not indicate any benefit from adding ammonium hydroxide to the preparation, an important factor discovered when molybdenum trioxide is reacted with 2-ethyl-1-hexanol.
In U.S. Pat. No. 4,434,975 to ARCO, investigators found that molybdenum catalysts could be made from saturated alcohols or glycols having one to four carbon atoms, such as ethylene glycol and propylene glycol, by reacting them with molybdenum metal and an organic hydroperoxide, peroxide, or H.sub.2 O.sub.2. Molybdenum compounds prepared by reacting an ammoniumcontaining molybdate with a hydroxy compound, for example, an organic primary or secondary alcohol, a glycol or a phenol, are described in U.S. Pat. No. 3,784,482 and 3,787,329 to Cavitt.
Further, U.S. Pat. No. 3,573,226 to Sorgenti discloses that molybdenum-containing epoxidation catalyst solutions may be made by heating molybdenum powder with a stream containing unreacted tertiary butyl hydroperoxide and polyhydric compounds of from about 200 to 300 molecular weight and having from 4 to 6 hydroxyl groups per molecule. These catalysts are used for the epoxidation of propylene according to U.S. Pat. No. 3,666,777 to Sorgenti.
U.S. Pat. No. 3,953,362 to Lines et al. reveals that novel molybdenum epoxidation catalysts may be prepared by reacting an oxygen-containing molybdenum compound with hydrogen peroxide and an amine and optionally water or an alkylene glycol at elevated temperatures. Similar catalysts are prepared by reacting an oxygen-containing molybdenum compound with an amine and an alkylene glycol at elevated temperatures according to U.S. Pat. No. 4,009,122 also to Lines et al.
U.S. Pat. No. 3,668,227 to Mattucci et al. also concerns molybdenum glycol catalysts prepared from molybdenum acetyl acetonate and isolated as solids. When the materials are used as epoxidation catalysts, they must be employed in solution with a hydrocarbon solvent. Molybdenum derivative compounds also useful as epoxidation catalysts may be prepared by reacting an oxygen-containing molybdenum compound such as molybdenum acetylacetonate, molybdic acids and molybdenum oxides with an organic compound having vicinal hydroxyl groups in the presence of a hydrohalic acid such as hydrofluoric acid, hydrochloric acid and the like, according to U.S. Pat. No. 3,991,090 to Hagstrom et al.
Kollar U.S. Pat. Nos. 3,860,662 and 3,947,500 disclose a modification of the epoxidation process wherein the epoxidation reactor effluent, which is acidic, is treated with a base such as sodium bisulfite or sodium hydroxide in order to decrease reaction product dehydration during the distillation of the reactor effluent.
In our laboratories the preparation and utilization of epoxidation catalysts has been studied. Copending Marquis et al. U.S. patent application Ser. No. 687,701, now U.S. Pat. No. 4,626,596, entitled "Synthesis of Molybdenum/Alkylene Glycol Complexes Useful as Epoxidation Catalyst" is directed to the provision of soluble molybdenum/alkylene glycol complexes by the reaction of an ammonium-containing molybdenum compound such as ammonium heptamolybdate tetrahydrate with a glycol such as ethylene glycol or propylene glycol. Copending Marquis et al. U.S. patent application Ser. No. 804,132, now U.S. Pat. No. 4,654,427 entitled "Synthesis of Molybdenum Oxide/Alkanol Complexes" discloses the preparation and utilization of soluble molybdenum catalysts made by reacting a molybdenum oxide with an alkanol in the presence of ammonium hydroxide. Copending Marquis et al. U.S. patent application Ser. No. 804,131, now U.S. Pat. No. 4,650,886 entitled "Synthesis of Ammonium Molybdate/Alkanol Complexes" is directed to the preparation and utilization of soluble molybdenum catalysts prepared by reacting an alkanol with an ammonium molybdate.
Although the results obtained have been generally satisfactory, there is still need for improvement.